Land preparation and planting of soya bean


IN this episode of our series on soya bean production, we shall continue to discuss some of the best ways to grow soya bean.
Previous instalments have covered soils and agro-ecological factors such as rainfall, temperatures and periods of sunshine, making summer the best time to grow soya bean.
We saw that yields increase as we move from loamy sands to heavy clays and as rainfall increases from a minimum of around 600mm and up.
We also covered some aspects on required inputs but we shall revisit that aspect again later.
This episode will focus on land preparation and planting with emphasis on the operations required to ensure good germination and optimum plant populations.
This information will assist those readers intending to take up soya bean production but is not a substitute for formal training sessions that we expect to be given to all farmers joining the Command Soya bean Programme this coming cropping season.
Land preparation is the most important first step in growing a soya bean crop.
Land preparation must make the field weed-free with a fine tilth that is free of excessive crop residues and large clods (magadhi).
This step will determine whether the farmer gets ‘sora’ beans, ‘sorry’ beans or real soya beans.
Land preparation equipment includes ploughs, rippers, row markers and disc harrows for motorised systems.
Small-scale producers use animal-drawn implements such as ploughs, harrows and row markers. Two and four-wheel low power (8-20HP) tractors that use very low amounts of fuel are available for small to medium-scale farmers.
These are no-till units that plant, apply fertiliser and herbicides in one operation bringing down fuel consumption from as high as 30l/ha to just over 5l/ha.
Herbicides are then used to clean up any weeds present at the time of planting.
This is the Conservation Agriculture approach which promotes minimum disruption of soil structure to reduce soil degradation.
Let us return to conventional tillage practices.
In virgin soils where no crops have been grown before, the first step is land clearing. This may involve stumping (kuchera magobo) followed by ripping and then disking.
Alternatively, deep ploughing can be done after stumping. Ploughed lands may need to be disked when moist to obtain a fine tilth.
A spike harrow can also be used to break up large clods before planting. Farmers are encouraged to minimise the number of runs over the field as fuel costs will go up, eating into profits. Soils get compacted, becoming less productive if they are constantly run over by motorised equipment.
For soya bean, it is extremely important to do a thorough land preparation, for two reasons.
First, if the field is free of large clods, germination will be good, giving an optimum plant population for the highest possible yield.
Second, weed control will be easier if one starts with a clean field.
Land preparation can be done soon after harvest as a ‘winter plough’.
Weeds may grow in the ploughed or disked fields during the dry season (chirimo). Do we plough again? No, that will waste fuel, time and also destroy our soil structure.
We can apply glyphosate, commonly called Round-up, a non-selective herbicide that will kill and clean up all the green weeds before planting.
A word of caution to farmers: Exercise great care with pesticides. Read the container label!
When using animal-drawn implements for land preparation, the procedures are similar.
Ploughing must be done to bury the emerging weeds and the crop residues from the previous season as well as to create a fine seedbed for the new crop to be planted.
Planting furrows are cut and seeds planted by hand. Labour is critical for timely hand-planting.
If labour and herbicides are available, ploughing can be omitted.
Instead planting furrows can be cut into moist ground at 40 to 50 cm between rows and 4 -5 cm deep using an ox-plough or a cultivator with all tines removed except the two outer ones that act as row markers.
Seeds and fertilisers are dribbled into the furrows at appropriate rates and covered up immediately with tree branches or a spike harrow.
Again weeds can be cleaned up with Round-up before the crop germinates. And again great care must be exercised with pesticides!
Alternatively, in some cases, the soyabean can be planted first, followed by herbicide application. By the time the crop germinates, the weeds will be dying out.
This is the case where a no-till planter is used. Once the soil is judged to be well-soaked (20-30 mm rainfall), the no-till planter goes in.
It has sharp blades that cut through the stubble of weeds and crop residues, deep into the soil, placing seed and fertiliser at the appropriate depth and covering up.
Again green weeds already growing can be killed using Round-up. No till planters drawn by two-wheel tractors are now available and can plant 3 to 5 ha per day, using as little as 5l/ha.
To be continued next week.


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